A heat transfer model to predict superheated and saturated condensation of HFC/HFO refrigerant mixtures

This work proposes a new heat transfer model for superheated and saturated condensation for low global warming potential refrigerant (GWP) mixtures with hydrofluorocarbons (HFC) and hydrofluoroolefins (HFOs) constituents, and validates it with experimental data. The superheated condensation region exists upstream of the saturated region, and has been traditionally modeled as single-phase flow. However, prior research on pure fluids has shown that the heat transfer coefficients in this region are significantly higher than those associated with single-phase flow. Accurately modeling superheated condensation allows for the design of a more compact heat exchanger. In the model, the mixture effects associated with zeotropic condensation were accounted for using the equilibrium Silver, Bell and Ghaly method. The model was validated with condensation data for five low GWP refrigerant mixtures (R448A, R450A, R452A, R454B, and R454C). A total of 962 data points were compared and the resulting mean absolute percent errors (MAPEs) were equal to 8% and 12% for superheated and complete condensation, respectively. Furthermore, past investigations of pure fluids have noted an enhancement in heat transfer in the subcooled condensation region, which exists downstream of the saturated region. However, in the current study, the enhancement due to latent effects was not observed in the subcooled region and the heat transfer was well predicted (MAPE = 18%) by a single-phase correlation.